1. Field of Invention
This invention relates in general to fuses, and in particular to high power case fuses.
2. Background of Related Art
High power distribution box fuse assemblies used in vehicles commonly include a nonconductive housing encasing a conductive set of female terminals (i.e., fuse body). The set of female terminals are joined by a fuse element disposed therebetween. The female terminals are inserted over a set of male blade terminals extending from the power distribution box for completing an electrical circuit. The female terminals are typically designed with a spring-type feature to maintain a strong electrical contact with the male terminal blades. If the current draw of the electrical circuit increases above a predetermined current threshold, the fuse element will open thereby terminating current flow across the respective set of female terminals.
Copper which is has good electrical conductivity properties is preferably used to produce the fuse body; however, copper is susceptible to relaxation as temperature increases. That is, as the current drawn in the electrical circuit increases, so does the temperature. In response to the temperature increase, copper has a tendency to relax. As a result, the clamping portion of the fuse body for maintaining a tight connection with the male terminal blades (e.g., the spring-type future of the female terminals) relaxes thereby decreasing the overall contact area which reduces electrical conductivity (i.e., increases resistance).
Since the fuse body is encased within the housing, the thickness of the female terminals (i.e., the springs) is limited to a predetermined size due to packaging constraints. As a result, the footprint of the fuse body is limited such that additional material is prevented from being added to strengthen the spring-like features for maintaining contact with the male terminal blades. As a result, copper alloy having lower conductivity properties is typically substituted for the copper-based material having higher conductivity properties to produce the fuse body. The relaxation properties for copper alloy having low conductivity properties occur at much higher temperatures as compared to copper. Therefore, a desired contact area between the female terminals and the male terminal blades can be maintained at elevated temperatures using the copper alloy in comparison to copper-based material having higher conductivity properties. The disadvantage is that the copper alloy has lower conductivity properties in comparison to copper-based material. As a result, the fuse assembly, given the perspective footprint, are limited to 60 amps or less.